This invention relates to an air meter, particularly to an air meter for measuring air mass flow suitable for the use of engine control for an automobile.
As the prior art air meter, a ratio-metric output type air meter is known having an output characteristic adjusting circuit and a ratio-metric converting circuit, as shown in Japanese Patent Prepublication No. 148556/1998. Also, in a frequency output type air meter, a ratio-metric output type air meter is known having an output characteristic adjusting circuit and a voltage controlled oscillator circuit.
However, in both of the ratio-metric output type air meter and the frequency output type air meter, two circuits of the respective air meters have independent internal reference power supply circuits, and to assure their accuracy it is necessary that a resistor is connected to the external of a monolithic IC, and therefore, it is necessary that the IC has connection terminals of the number proportional to the number of the internal reference power supply circuit outputs.